The present invention relates to a welding wire, constituted by a core of welding powder enclosed by a mantle of metal, to be used for automatic or semi-automatic welding, with or without a protective gas, as well as to a method of manufacturing such a welding wire.
While the wire throughout the specification and claims is called a welding wire, it is to be understood that this wire may also be used for soldering or hard surfacing.
It is known in the art to use a welding wire which is composed of an outer metallic sheath and a core of powder surrounded by this sheath. The cylindrical or polygonal sheath is usually formed from a band of steel, which may or may not be alloyed, or from another metal which contributes to the welding. The core of the welding wire, which constitutes usually 10 to 50% of the total weight of the wire is composed of a pulverulant mixture usually comprising a plurality of the following components in different combinations in accordance with the work to be performed and in accordance with the conditions prevailing during the welding. Such components may include a slag-forming material of an oxide base and/or carbonates of alkaline earth metal, a flux-forming material of fluoride base and/or alkaline halogenides or alkaline earth metals, deoxidizing and denitrating metals such as Al, Mg. Si, Ti, Mn and different alloys of such metals, one or a plurality of products for stabilization of the welding arc, for example a titanium base of calcium or potassium, a support material of ferric base, of ferro alloys or other metals and alloys to form the desired welding composition. Other mineral and metallic products may be included in the composition of the powder, but since the specific composition of the powder does not form part of the present invention, the above enumeration of such compositions is considered to be sufficient.
A process of fabricating such a welding wire with a core of powder is also known in the art which consists to transform a continuous metallic band into a channel, to introduce the pulverulant mixture in such a channel, to form the channel by one or a plurality of rolling or drawing operations into a tubular member enclosing the powder and to close the metallic member, by forming a weld seam connecting the longitudinal edges, before proceeding with the final drawing operation to impart to the thus-formed welding wire the desired diameter.
This known process to fabrication has considerable drawbacks in that the powder tends to disperse and to stick to the bent borders of the channel during closing of the same and to stick especially to these borders during connecting the borders of the channel by soldering or welding. This will result in a joint of the borders by soldering or welding of such poor quality that the final transformation of the filled tube by drawing is rendered very difficult and the diameter of the thus-formed welding wire can therefore be reduced by drawing only to a small extent.
Various solutions to overcome this drawback are known in the art. A first solution consists to reduce the amount of powder which is fed into the channel. This of course leads to a corresponding increase of the ratio of solid metal to the powder in the welding wire thus obtained. Furthermore, this solution necessarily leads to difficulties in maintaining the homogeneity and uniform distribution of the powder during the fabrication and transformation of the tubular wire. The possibility to use such a welding wire having a disadvantageous ratio of powder to metal and an irregular quality are evidently very limited. Another solution, which likewise only partially solves the above pointed-out problem, consists to submit the powder distributed in the channel to an equalization and compacting prior to closing the tube blank. A further solution, which entails some complications in the technique of preparing the powder and the introduction thereof into the channel, consists to mix the powder with a binder and extrude the thus-formed plastic mass in form of a continuous preformed strand into the channel. This last-mentioned solution is burdensome and does not lend itself to competitive mass fabrication. Thus, all of the above-mentioned solutions have not found an industrial application for manufacturing tubular welding wires with a soldered or welded joint.
In the copending application Ser. No. 572,636 of which the present application is a continuation-in-part application, there is disclosed a method of forming a wire of the aforementioned kind in which the above shortcomings of such wires known in the art are essentially avoided by covering the powder after being introduced into an open channel of substantially U-shaped profile by a sheath which surrounds at least part of the powder and holds it at the bottom of the channel to keep it away from the end edges of the flanks, so that, after the channel is closed by bringing the end edges in abutment with each other, the powder is positively kept away from these end edges, whereby the latter may be welded to each other in a perfect manner and the cross-section of the thus-formed wire may subsequently be reduced by drawing operations or the like to a considerable extent.
However, the process as disclosed in the aforementioned application has still certain drawbacks, especially during reducing of the cross-section of the wire by a drawing or rolling operation since, in this process disclosed in the aforementioned application, the metallic mantle enclosing the core of powder has evidently a non-uniform thickness, in that about half of the circumference of the outer mantle is constituted only by the wall of the channel, whereas the other half is constituted by this wall and the covering sheath, which covers the powder before closing the channel. This non-uniform wall thickness of the outer mantle will cause certain difficulties during subsequent reduction of the cross-section of the wire.